1. Field of the Invention
The present invention generally relates to an apparatus and method for cleaning semiconductor wafers, and in particular to an apparatus for cleaning the wafers with less water consumption and a cleaning method for more effectively cleaning the wafers by means of four sets of water jet generating means arranged to be symmetric with respect to each other for generating water jets toward the wafers.
2. Description of the Prior Art
Semiconductor industry is a highly water-consuming industry in which a great amount of water is used to clean wafers. With the development and improvement of sub-micro meter semiconductor manufacturing techniques, the size of wafers and the number of semiconductor factories are being increased. Thus, the consumption of water is increased too. A major issue of the semiconductor industry is to reduce the water consumption for both economic and environmental purposes.
Conventionally, the wafers are placed in a rinsing bath, then pumping water and nitrogen gas continuously form the bottom into the bath, making the water overflowing out of the bath for cleaning wafers. The purpose for rinsing wafers is bringing debris and contaminant away from the surface of the wafers by overflowing water and preventing the wafers being second polluted in the cleaning process.
Two types of conventional wafer cleaning systems are known in the art. One is a plug-flow system and the other is CSTR system. Hybrid systems of the two systems are also known. The plug-flow system provides the most efficient way for cleaning wafers, while the CSTR system has a small size. However, both systems consume a great amount of water.
FIGS. 1 and 2 of the attached drawings show a conventional wafer cleaning apparatus 1 comprising a rinsing container 5 in which two parallel water pipes 21 and 22 are arranged. A gas pipe 3 is also arranged in the rinsing container 5 between the water pipes 21 and 22. One end of each water pipe 21 and 22 is closed with water fed into the pipe 21 and 22 through an opposite open end. Similarly, one end of the gas pipe 3 is closed with nitrogen gas fed into the gas pipe 3 through an opposite open end. A number of V-shaped notches are formed on the top edge of each side wall of the rinsing container for water overflowing and bringing debris and contaminant out of the rinsing container 5.
Wafers 4 to be cleaned are disposed into the rinsing container 5 by cassettes, trays, or racks. A gap of a predetermined width, such as 0.6 mm, is formed between adjacent wafers 4. Conventionally, fifth wafers are positioned in the rinsing container 5 in a batch to be simultaneously cleaned thereby.
Each water pipe such as pipe 21 is formed with two holes 211 and 212 spaced at a predetermined distance as shown in FIG. 3A. Water is fed into the rinsing container 5 through the holes 211 and 212. FIG. 3B is a cross-sectional view of the water pipe 21 in which the holes 211 are located in the fourth quadrant at 315 degree position, while the holes 212 are located in the third quadrant at 240 degree position.
As shown in FIG. 3C, holes 31 are defined in the gas pipe 3 at predetermined distance through which nitrogen gas is supplied into the rinsing container 5. The gas that is fed into the container 5 causes an up-rising water flow that moves into the gaps between the wafers to clean the wafers and move debris therefrom. However, due to the uncontrollable water flow in and out of the gaps between wafers, it often occurs that the wafers are not completely cleaned. Thus, extended cleaning period is required to have the wafers completely cleaned. This reduces the operation efficiency of the wafer cleaning apparatus and increases the consumption of water.
Furthermore, water must be kept flowing in the rinsing container in order to control or reduce the population of bacteria. In the plug-flow system, most of the water flows between the wafers and the side walls of the container rather than through the gaps between wafers. In addition, the water flow is often diverted at the edges of the wafers. Thus, the wafers cannot be effectively cleaned.
It is thus desirable to have a wafer cleaning apparatus capable to operate in more efficient manner with less consumption of water for overcoming the above mentioned problems.
Accordingly, an object of the present invention is to provide a wafer cleaning apparatus operable in a more efficient manner with less water consumption. The wafer cleaning apparatus includes multiple water jet generating means arranged to be symmetric with respect to each other for generating water jets toward a number of wafers to perform a wafer cleaning operation.
To achieve the above objects, in accordance with the present invention, there is provided a wafer cleaning apparatus comprising a rinsing container in which wafers to be cleaned are positioned and four sets of nozzles are arranged at four diagonal corners of a rinsing container to be alternately actuated for effectively cleaning wafers. In a first phase of the wafer cleaning process, the first nozzle set and the fourth nozzle set are turned on to generate water jets in diagonally opposite directions with respect to the wafers for a given period. In a second phase, the second nozzle set and the third nozzle set are turned on to generate water jets in diagonally opposite directions with respect to the wafers for a given period. In a third phase, the third nozzle set and the fourth nozzle set are turned on to cause an up-rising water flow from a bottom of the container to a top open side thereof for expelling contaminants dissolved or suspended in the water out of the container.
Preferably, in accordance with the present invention, the wafers to be cleaned are moved into the rinsing container by a receiving cassette, a supporting tray or a suspension frame that receives and retains the wafers therein. The wafers are arranged to have a primary surface thereof facing a center of the rinsing container.
Preferably, the nozzles are preferably controlled by a programmable logic control (PLC) based control device to generate water jets toward the wafers for performing a wafer cleaning process.